Heat transfer in natural convection

Chang, Y. P., 1957, A Theoretical Analysis of Heat Transfer in Natural Convection and in Boiling, Trans. ASME, J. Heat Transfer 79.1501 1513. (2)... 

Stephan, K. Bubble formation and heat transfer in natural convection boiling. In Hahne, E. Grigull, U. Heat transfer in boiling. Washington Hemisphere 1977, p. 3-20... 

Single-Phase Heat Transfer in Natural Convection.520... 

NA%TOAL CONVECTION TO AIR FROM VERTICAL SHAPES AND HORIZONTAL PLANES. Equations for heat transfer in natural convection between fluids and solids of definite geometric shape are of the form ... 

K. Stephan and J. Mitrovic, Heat Transfer in Natural Convective Boiling of Refrigerants and Refrigerant-Oil-Mixtures in Bundles of T-Shaped Finned Tubes, in Advances in Enhanced Heat Transfer—1981, R. L. Webb, T. C. Carnavos, E. L. Park Jr., and K. M. Hostetler eds., HTD vol. 18, pp. 131-146, ASME, New York, 1981. 

K. Stephan and P. Preusser, Heat Transfer in Natural Convection Boiling of Polynary Mixtures, in Proc. 6th Int. Heat Transfer Conference, Toronto, Canada, vol. 1, p. 187,1978. 

Metzner and Friend [Ind. Fng. Chem., 51, 879 (1959)] present relationships for turbulent heat transfer with nonnewtouiau fluids. Relationships for heat transfer by natural convection and through laminar boundaiy layers are available in Skelland s book (op. cit.). 

Coefficients of heat transfer by natural convection from bodies of various shapes, chiefly plates and cylinders, are correlated in terms of Grashof, Prandtl, and Nusselt numbers. Table 8.9 covers the... 

Under what conditions is heat transfer by natural convection important in Chemical Engineering ... 

Due to the fact that density differences can only have an effect when associated with acceleration due to gravity, both (3AT and p/p0 are consistently combined with the Galileo number Ga = Re2/Fr = g l3/v2. Therefore, in the heat transfer under natural convection the... 

Heat transfer by natural convection across an enclosed space, called an enclosure or, sometimes, a cavity, occurs in many real situations, see [34] to [67]. For example, the heat transfet between the panes of glass in a double pane window, the heat transfer between the collector plate and the glass cover in a solar collector and in many electronic and electrical systems basically involves natural convective flow across an enclosure. 

Heat transfer by natural convection across porous media-filled enclosures occurs in a number of oractical situations and will be considered in this sectif T 6] to f511... 

Dropkin, D., and E. Somerscales Heat Transfer by Natural Convection in Liquids Confined by Two Parallel Plates Which Are Inclined at Various Angles with Respect to the Horizontal, J. Heat Transfer, vol. 87, p. 71, 1965. 

The presence of a temperature gradient in a fluid in a gravity field always gives rise to natural convection currents, and thus heat transfer by natural convection. Therefore, forced convection is always accompanied by natural convection. 

A 15 -cm-widc and 18-cm-high vertical hot surface in 25 C air is to be cooled by a heat sink with equally spaced fins of rectangular profile. The fins are 0.1 cm thick and 18 cm long in the vertical direction. Determine the optimum fin height and the rate of heat transfer by natural convection from the heat sink if the base temperature is SS C. 

Coefficients of heat transfer by natural convection from bodies of various shapes, chiefly plates and cylinders, are correlated in terms of Grashof, Prandtl, and Nusselt numbers. Table 8.9 covers the most usual situations, of which heat losses to ambient air are the most common process. Simplified equations are shown for air. Transfer of heat by radiation is appreciable even at modest temperatures such data are presented in combination with convective coefficients in item 16 of this table. 

Convection is the transfer of heat from one point to another within a fluid by the mixing of one portion of the fluid with another. In natural convection, the motion of the fluid is caused by gradients of temperature and gravity. In forced convection, the motion is caused by mechanical means that enhance the rate of heat transfer over natural convection. An example of convection drying would include the use of hot air in tray dryers and fluid bed dryers. 

Calderbank and Moo-Young also confirmed the classical correlation for mass and heat transfer through natural convection in dispersions of fine droplets or fine gas bubbles for so-called rigid spheres" ... 

Another distinction among flows is whether the flow is forced by an external means such as a pump (termed forced convection) or whether the flow arises as a result of a density difference developed in the fluid circuit as a result of the heat transfer (termed natural convection or thermosiphon action). Some cases include both mechanisms. 

Equations are presented in this section for evaluating the heat transfer by natural convection from the external surfaces of bodies of various shapes. The correlation equations are of the form described in the section on the heat transfer correlation method, and the orientation of the surface is given by the surface angle defined in Fig. 4.4. Supporting experimental evidence for each such equation set is outlined after each equation tabulation. The correlations are in terms of Nu, Ra, and Pr, parameters that involve physical properties, a length scale, and a reference temperature difference. Rules for the evaluation of property values are provided in the nomenclature, and the relevant length scale and reference temperature difference are provided in a separate definition sketch for each problem. 

Circular Isothermal Fins on a Horizontal Tube. Tsubouchi and Masuda [269] measured the heat transfer by natural convection in air from circular fins attached to circular tubes, as in the configuration shown in Fig. 4.23/ Correlations for the heat transfer from the tips of the fins (see the figure for definition), and from the cylinder plus vertical fin surfaces, were reported separately. 

Enclosure problems (Fig. 4.1c) arise when a solid surface completely envelops a cavity containing a fluid and, possibly, interior solids. This section is concerned with heat transfer by natural convection within such enclosures. Problems without interior solids include the heat transfer between the various surfaces of a rectangular cavity or a cylindrical cavity. These problems, along with problems with interior solids including heat transfer between concentric or eccentric cylinders and spheres and enclosures with partitions, are discussed in the following sections. Property values (including P) in this section are to be taken at Tm = (Th+ TC)I2. 

N. Seki, S. Fukusako, and H. Inaba, Heat Transfer of Natural Convection in a Rectangular Cavity With Vertical Walls of Different Temperatures, Bull. JSME (21/152) 246-253,1978. 

Gravitational settling of particle in fluid Flow of viscoelastic fluid Pressure and momentum in fluid Unsteady state heat transfer/mass transfer Fluid flow with free surface Gravitational settling of particle in fluid Heat transfer by natural convection Heat transfer to fluid in tube Flow of fluid exhibiting yield stress... 

Natural convection heat transfer occurs when a solid surface is in contact with a gas or liquid which is at a different temperature from the surface. Density differences in the ffuid arising from the heating process provide the buoyancy force required to move the ffuid. Free or natural convection is observed as a result of the motion of the fluid. An example of heat transfer by natural convection is a hot radiator used for heating a room. Cold air encountering the radiator is heated and rises in natural convection because of buoyancy forces. The theoretical derivation of equations for natural convection heat-transfer coefficients requires the solution of motion and energy equations. 

An estimate of the rate of heat transfer from the ullage gas to the container walls is necessary to calculate the equivalent condensed mass. During brief periods of high gas flow, heat transfer occurs by forced convection. When the rate of constant pressure transfer is slow, a natural convection mechanism is more important. A model suggested here circumvents many of the problems introduced by the separate consideration of forced and natural convection of the pressurizing gas. It is assumed in this model that the predominant mode of heat transfer is natural convection. 

Convection involves the transfer of heat by the motion and mixing of macroscopic portions of a fluid (i.e., the flow of a fluid past a solid boundary). The term natural convection is used if this motion and mixing is cansed by density variations resnlting from temperature differences within the fluid. The term forced convection is used if this motion and mixing is cansed by an outside force, such as a pump or fan (as shown in Figure 6.4). The transfer of heat from a hot-water radiator to a room is an example of heat transfer by natural convection. The transfer of heat from the surface... 

Bhattachaijee, D. and V. Kothari, Prediction Of Thermal Resistance of Woven Fabrics. Part II Heat transfer in natural and forced convective environments. Journal of the Textile Institute, 2008, 99(5), 433 49. 

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